Amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease) is an age-dependent neurodegenerative disorder characterized by the progressive selective death of motor neurons. Approximately 10% of ALS patients are familial cases and more than 90 mutations in the gene encoding copper-zinc superoxide dismutase (SOD1) have been linked with approximately 25% of familial ALS. The long term objective of this project is to understand how SOD1 mutants lead to motor neuron degeneration in familial ALS. It has been proposed that mitochondrial dysfunction and activation of apoptosis play a central role in motor neuron death. However, the molecular mechanisms leading to mitochondrial dysfunction and apoptosis are incompletely understood. The innovative aspect of this project is to use a combination of proteomic and biochemical approaches to study mutant SOD1 mediated mitochondrial apoptosis. Specific Aim 1 is to identify mitochondrial proteins that are targets of the toxicity associated with SOD1 mutants by proteomics analysis of cellular models of ALS. Specific Aim 2 is to study the functional roles of the identified target proteins in mitochondrial dysfunction, activation of apoptosis and neuron death. Our preliminary results have shown a mitochondrial outer membrane protein named "voltage dependent anion channel 2 (VDAC2)" as a promising target and this protein will be studied in detail. Similar experiments designed for this protein will be carried out for other proteins as more targets will be identified in Aim 1. Specific Aim 3 is to determine the functional differences in the identified target proteins between motor neurons and other cell types from the spinal cord of the ALS transgenic mice. The differences of target proteins such as VDAC2 between motor neurons and other types of cells from the mouse spinal cord will be measured in terms of mRNA levels, protein abundances and modification state. The relationship between the changes in the target proteins and mitochondrial apoptosis, age-dependent pathological changes and disease progression will also be investigated. The studies of functional differences of these proteins between motor neurons and other cell types are likely to provide insights into the mechanisms leading to selective motor neuron death.